1. Field of the Invention
This invention relates to a signal processing arrangement having particular though not exclusive application in Doppler radio navigation systems where bearing information is coded in terms of frequency.
2. Description of the Prior Art
Doppler radio navigation systems have previously been described in British patents 1,225,190 and 1,234,541, and elsewhere in the technical literature. In such systems, a radio frequency source is commutated successively to the separate elements of a linear array of radiators, while a slightly offset frequency is transmitted from a reference antenna. Direction (angle of reception) from the array is basically defined by the frequency of the commutated wave emitted in that direction. In an azimuth system using a horizontal array, bearing information over a sector of typically .+-.60.degree. normal to the axis of the array can be provided. Accordingly, the frequency-counting receivers of the cooperating remote (receiving) station must accept a band of frequencies corresponding to the complete sector of possible bearings. Such received bearing information signal does not consist of only the discrete information frequency (by direct propagation) but also includes multipath components (by reflection).
In the said system receiver, therefore, a signal processor is required to track the valid information signal spectrum, and to be able to discriminate against multipath signals.
To fulfill these requirements, the processor must provide scanning verification and narrow-band tracking filter facilities and in its application to Doppler radio navigation system receivers, the signal processing arrangement of the present invention must provide these functions.
The manner in which the present invention deals uniquely with these problems to provide a novel arrangement will be understood as this description proceeds.